[Feature request] Add RetroAchievements support

[Svipur]

Via rcheevos.

The rudimentary list of requirements is found here: https://docs.retroachievements.org/System-X-wen/#requirements

The current list of identified issues with the FUSE core is found here under the system ID 59: https://docs.retroachievements.org/Emulator-Support-and-Issues/#unsupported-consoles

[leiradel]

From the list of requirements:

• Requires rcheevos memory map to leverage memory descriptors
  • I believe RALibretro supports Libretro's memory descriptors, which are already implemented in the Fuse core
• Requires ability to map keyboard to port 3 (RALibretro)
  • Not sure what this means, but RALibretro could easily force the keyboard in the input port 3 for this core
• Uncertain about save support; cannot seem to insert save disk
  • Save state support is implemented in the core

So it seems it only needs to be implemented in RALibretro.